(a) Technical Field
The present disclosure relates generally to a method and a system for controlling charging and discharging for a hybrid vehicle, and more particularly, to a method and system for controlling charging and discharging for a hybrid vehicle that may consume regenerative electric power collected by a motor through regenerative braking during coasting of the hybrid vehicle when operating an integrated starter-generator (ISG) according to a state of charge (SOC) of a battery.
(b) Description of the Related Art
Hybrid vehicles operate through the use of power from an internal combustion engine and power from a battery. In particular, hybrid vehicles are designed to efficiently combine and use power of the internal combustion engine and the motor. For example, as illustrated in FIG. 1, a hybrid vehicle includes: an engine 10; a motor 20; an engine clutch 30 which controls power connection between the engine 10 and the motor 20; a transmission 40; a differential gear unit 50; a battery 60; an integrated starter-generator (ISG) 70 which starts the engine 10 or generates electric power by output of the engine 10; and wheels 80.
As further shown, the hybrid vehicle includes: a hybrid control unit (HCU) 200 for controlling an overall operation of the hybrid vehicle; an engine control unit (ECU) 110 for controlling an operation of the engine 10; a motor control unit (MCU) 120 for controlling an operation of the motor 20; a transmission control unit (TCU) 140 for controlling an operation of the transmission 40; and a battery control unit (BCU) 160 for managing and controlling the battery 60. The BCU 160 may also be referred to as a battery management system (BMS). The ISG 70 may also be referred to as a starting/generating motor or a hybrid starter-generator (HSG).
The hybrid electric vehicle may be driven in a driving mode, such as an electric vehicle (EV) mode, which is a mode of a true electric vehicle solely using power of the motor 20; a hybrid electric vehicle (HEV) mode using torque of the motor 20 as auxiliary power while using torque of the engine 10 as main power; and a regenerative braking (RB) mode collecting braking and inertia energy through power generation of the motor 20 to charge the battery 60 during braking or driving using the inertia of the vehicle. The motor 20 of the hybrid vehicle generally operates as a generator for collecting the inertia energy during the regenerative braking (RB) mode. The running by inertia energy of the hybrid vehicle may be referred to coasting.
As shown in FIG. 2, by setting a minus torque to the motor while coasting, the inertia energy may be collected as regenerative electric power. When the motor operates as a generator, the regenerative electric power generally charges the battery of the hybrid vehicle. However, when the battery is in a fully charged state such that charging is limited or in an over-temperature state, the regenerative electric power from the motor 20 cannot charge the battery.
When the battery is in the fully charged state during coasting, a conventional method known in the related art performs fuel-cut control instead of the regenerative braking so as to use a friction torque (minus torque) of the engine, as shown in FIG. 3. Because the friction torque of the engine while the fuel is cut is transmitted to an axle through the engine clutch, the same drivability as during the regenerative braking by the motor may be accomplished. However, the friction torque cannot be varied, and when the shift gear of the transmission is changed, drivability may rapidly deteriorate.
Further, in another conventional method known in the related art, when the battery is in the fully charged state during coasting, the regenerative electric power of the motor produced by the regenerative braking is consumed by an air conditioner or heater 90. However, due to the unwanted operation of the air conditioner or heater, the temperature in the hybrid vehicle may be changed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the related art that is already known to a person of ordinary skill in the art.